Method and an apparatus for controlling a car equipped with an automatic transmission having a lockup clutch

ABSTRACT

A method and an apparatus for controlling a car equipped with an automatic transmission having a lockup clutch. According to the control method when the lockup clutch is in the lockup state, a variation of a generated torque is detected. When the range of the torque variation detected exceeds a predetermined value, an engine torque is reduced by controlling the engine, and the automatic transmission is controlled to compensate for a reduction of the driving torque due to a reduction of the engine torque. Thus, the speed change ratio is changed to the low gear side. The control unit includes a unit for controlling an output torque of an engine according to a command value, a unit for changing the transmission ratio of the automatic transmission, a unit for detecting a variation of the engine torque, a unit for deciding a target driving torque, a unit for reducing a torque command value when the range of a detected variation of the torque has exceeded a predetermined value when the lockup clutch was in the lockup state, and a unit for deciding a transmission ratio at which the reduction of the driving torque due to the reduction of the engine torque is compensated for.

This is a divisional of application Ser. No. 08/025,211, filed Mar. 2,1993 U.S. Pat. No. 5.468,196.

BACKGROUND OF THE INVENTION

In a car equipped with an automatic transmission having a lockup clutch,the present invention relates to a method and an apparatus forcontrolling the car which controls both the engine and the automatictransmission to improve the fuel economy of the car and provide ofcomfortable riding of the car.

An automatic transmission equipped with a torque converter has aslipping loss due to the torque converter and has, therefore, adisadvantage of higher fuel consumption as compared with a manualtransmission equipped with a mechanical clutch. As a result, there hasbeen an increasing tendency that an automatic transmission having alockup clutch built into the torque converter is being used to have animproved fuel economy of the car.

A lockup clutch mechanically transmits an engine torque directly to thetransmission with a clutch except for starting or slow speed running ofa car, to thereby avoid a slipping loss of a fluid in the torqueconverter. Accordingly, when the lockup clutch is being engaged (lockedup), a torque is transmitted from the engine to the car shaft withoutthe fluid so that fuel economy of the car can be improved.

From the viewpoint of improving the fuel economy, it is moreadvantageous that the car speed, when the lockup clutch is engaged, isset as low as possible. However, if a car is abruptly accelerated fromthe state of a low engine speed in a lockup state, there occurs anextreme torque variation, which makes it difficult for the fluid toabsorb the torque variation, and a vibration occurs in the drive trainas a result. This vibration is transmitted to the car body to generate acar body vibration and a booming noise within the passenger room.Accordingly, although a lockup at the time of a slow speed operation isdesirable from the viewpoint of the fuel economy, the car speed when thelockup operation is started is limited from the viewpoint of therestriction of a car body vibration (torque variation).

A lockup control of the torque converter is disclosed in the JapanesePatent Unexamined Publication No. JP-A-61-136057 dated Jun. 23, 1986,for example. According to the invention disclosed in this publication, alockup is cancelled when a torque variation has occurred.

According to the conventional automatic transmission, there has been awide operation area in which the torque converter is used in a slippingstate, or a lockup cancelled state, which has resulted in a small effectof improvement in the fuel economy due to the lockup clutch.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the fuel economy ofthe car equipped with an automatic transmission having a lockup clutchand to improve the drivability of the car.

It is appropriate to define terms which are used in the specification ofthe present invention, before entering the description of the invention.In the present specification, "an output torque of the engine (an enginetorque) refers to "a torque obtained by the output shaft of the engine"and "a driving torque" refers to "a torque obtained by the output shaftof the transmission".

In the present invention, both the engine and the automatic transmissionare controlled. The engine is controlled so that a variation of theengine torque is restricted under the operating condition in which thefuel consumption is the minimum. At the same time, the automatictransmission is controlled so that the transmission rate is controlledto obtain a requested driving torque or the lockup is cancelled to avoidan engine stall.

According to the present invention, it is possible to set the lockupoperation starting point at a low speed side and at the same time it ispossible to restrict a car body vibration in the lockup at the slowspeed operation and to restrict a booming noise.

According to control unit for a car of the present invention, when adriver has started operation of an accelerator pedal, a target drivingtorque of the car which corresponds to the level of depression stroke ofthe accelerator pedal is determined. Based on the target driving torque,the transmission rate of the transmission and the target output torqueof the engine are determined. Based on the target engine torque, thethrottle valve opening of the engine is decided. The automatictransmission and the engine are controlled with the actuator so that thedecided transmission rate and throttle value opening can be obtained.

According to one embodiment of the present invention, a variation of theengine torque or a variation of the shaft torque is detected during theabove-described torque control when the lockup clutch is in the lockupstate. When the variation of the engine torque (shaft torque) exceedsthe reference value, the engine operation is controlled in the directionto lower the current engine torque and thus restricts the vibration ofthe car body. Further, at the same time when the engine torque iscontrolled, the transmission rate of the automatic transmission ischanged to a lower geared position, to compensate for a reduction of theengine torque, and thus maintains the driving torque of the car.

According to another embodiment of the present invention, in a carmounted with an engine in the air-fuel ratio controlling, engagement ordisengagement of the lockup clutch is selectively decided according tothe condition of the air-fuel ratio in operation. The car has a memoryfor storing a map which shows the operation area of the air-fuel ratiowhich can be locked up. The map shows an iso-air/fuel ratio chart withthe engine torque and the engine speed as the parameters. When thevalues of the engine speed and the engine torque are given, the air-fuelratio can be determined from the map. The lockup clutch is controlledaccording to the decision of whether the air-fuel ratio is under thelockup condition or not.

According to still another embodiment of the present invention, theactual air-fuel ratio is directly detected by the sensor. Thisembodiment is provided with a memory which stores areas of the air-fuelratios for the cases that the lockup clutch is engaged and dis-engaged.A decision is given as to which condition within the memory the measuredair-fuel ratio matches. The lockup clutch is controlled based on theresult of the decision of whether the air-fuel ratio falls under thelockup condition or not.

According to still another embodiment of the present invention, a memorywhich stores a map that shows an engine operation area in which thelockup clutch is engaged. Such engine operation area is indicated by theengine torque and the car speed as parameters. The engine torque and thecar speed are detected, and the lockup clutch is controlled according tothe decision of whether the engine is operated under the area of thelockup condition in the map.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for showing the basic concept of the controlof a car according to the present invention;

FIG. 2 is a block diagram for showing the torque-transmission ratecontrol system according to the present invention;

FIG. 3 is a block diagram for showing an embodiment of thetorque-transmission rate control system according to the presentinvention;

FIG. 4 is a map for showing the relationship between the car speed andthe driving torque;

FIG. 5 is a map for showing the relationship between-the air-fuel ratioand the engine torque;

FIG. 6 is a flowchart consisting of FIGS. 6A and 6B for showing themethod for controlling the relationship between the torque and thetransmission rate;

FIG. 7 is a timechart for showing the change of the signal of each partwhen the control of FIG. 6 is actually carried out;

FIG. 8 is a driving force line diagram for showing the case where theengine and the transmitter are combined;

FIG. 9 is a configuration diagram of the transmission when two sets ofCVT are connected;

FIG. 10 is a curve diagram for showing the efficiency of the torqueconverter;

FIG. 11 is a flowchart for showing the control when the torque converteris to be operated at the maximum efficiency;

FIG. 12 is a timechart for showing the change of the signal of eachportion when the control of FIG. 11 is actually carried out;

FIG. 13 is a diagram for showing the control of FIG. 12 in the drivingforce line diagram;

FIG. 14 shows the configuration of the hybrid transmission in which thegear of a fixed speed change rate and a CVT are combined;

FIG. 15 is a line diagram for showing the driving force of the hybridtransmission shown in FIG. 14;

FIG. 16 is block diagram for showing the hydraulic pump control systemwhich drives the torque converter having a lockup clutch and thetransmission;

FIG. 17 is a system for driving the starter, the oil pump and thecooling fan with one motor;

FIG. 18 is a block diagram for showing the control system of a carequipped with an automatic transmission having a fixed gear ratio;

FIG. 19 is a block diagram for showing further details of the embodimentshown in FIG. 18;

FIG. 20 is a part of the control flowchart in another embodiment of thepresent invention;

FIG. 21 is a part of the control flowchart in the above anotherembodiment of the present invention which is to be combined with theflow of FIG. 20;

FIG. 22 is a part of the control flowchart in the above-describedanother embodiment of the present invention which is to be combined withthe flow of FIG. 20 and FIG. 21;

FIG. 23 is a control flowchart of the fuel flow quantity and theignition timing according to the control method of the presentinvention;

FIG. 24 is a flowchart for showing an embodiment of the control of thecancellation (disengagement) of the lockup clutch;

FIG. 25 is a flowchart for showing another embodiment of the control ofthe cancellation of the lockup clutch;

FIG. 26 is a flowchart for showing another embodiment of the control ofthe cancellation of the lockup clutch;

FIG. 27 is a flowchart for showing another embodiment of (he control ofthe cancellation of the lockup clutch;

FIG. 28 is a timechart for showing the change of the signal of eachportion when the lockup clutch is engaged;

FIG. 29 is a flowchart for showing an embodiment of the control ofengaging the lockup clutch;

FIG. 30 is a timechart which compares the signal changes of each portiondepending on presence or absence of the lockup clutch;

FIG. 31 is a timechart which compares the signal changes of each portiondepending on presence or absence of the lockup clutch;

FIG. 32 is a timechart which shows the signal change of each portion incontrolling a booming noise when the lockup clutch is engaged;

FIG. 33 is a flowchart for showing an embodiment for controlling torquevariation;

FIG. 34 is a flowchart for showing another embodiment for controllingtorque variation;

FIG. 35 is a flowchart for showing another embodiment of the control ofthe engaging and disengaging of the lockup clutch;

FIG. 36 is a flowchart for showing another embodiment of the control ofthe engaging and disengaging of the lockup clutch;

FIG. 37 is a flowchart for showing still another embodiment of thecontrol of the engaging and disengaging of the lockup clutch; and

FIG. 38 shows an engine efficiency diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram for showing the basic configuration of thetorque control system of the car equipped with an automatic transmissionhaving a lockup clutch according to the present invention. When anautomatic transmission 1 is in the lockup state, a variation of theoutput torque of engine 2 is detected by a torque variation detectingunit 3. When the variation of the engine torque (or a shaft torque) hasexceeded a reference value as a result of an acceleration operation madeby the driver when the driver depressed the accelerator pedal furthermore while the engine 2 was operating at a relatively low speed, thetorque variation detecting unit 3 produces an output signal. Thereference value is set in advance on the basis of the level at which avalue of a torque variation causes a booming noise in the car.

A torque variation controlling unit 4 produces a signal for instructinga reduction of the engine torque to a unit 5 which controls the enginetorque in response to the occurrence of the output signal of the torquevariation detecting unit 3. At the same time, the torque variationcontrolling unit 4 produces in a transmission rate control actuator 6 asignal for changing the transmission rate of the automatic transmission1 to compensate for a reduction of the driving torque due to a reductionof the engine torque, and applies this signal to the automatictransmission 1. The automatic transmission 1 changes the speed changerate to the lower geared position.

The torque variation detecting unit 3 of the engine 2 includes a torquesensor. In addition to the torque sensor, other units for detecting atorque variation calculate a torque based on the output of a caracceleration sensor, differentiate the car speed and detect a speedchange of a ring gear. A unit 5 for controlling the engine torqueincludes a fuel injector 51 for controlling the fuel supply quantity anda throttle actuator 52 for controlling the intake air flow. Further, theunit 5 for controlling the engine torque may also include an ignitiontiming control-unit, a valve timing control unit and a variabledisplacement unit or an EGR control unit. The automatic transmission 1may include a non-stage transmission (CVT) which can continuously varythe speed change rate or a transmission which has a few or more stagesof fixed gear ratios.

When the load of the driving system can not absorb all the engine torqueat the moment when the driver has suddenly released the acceleratorpedal to reduce the engine speed while the engine 2 was operating at arelatively low speed in the lockup state of the automatic transmission1, there is a risk of an engine stall. Particularly in the case of alean burn engine, the engine generates relatively low output torque inthe lean burn operation area, and thus there is a high possibility of anoccurrence of an engine stall. In this case, the torque variationcontrolling unit 4 produces a signal for instructing an increase of theengine torque to the unit 5 for controlling the engine torque. At thesame time, the torque variation controlling unit 4 applies to the speedchange rate control actuator 6 a signal for changing the transmissionratio of the automatic transmission 1 to restrict the increase of thedriving torque due to an increase of the engine torque, or produces asignal for disengaging the lockup clutch and applies this signal to theautomatic transmission 1.

By the control system shown in FIG. 1, even if the car speed, at whichthe lockup clutch is engaged, has been set to the low speed side, it ispossible to simultaneously control the engine torque and thetransmission ratio, to prevent both a booming noise when the automatictransmission is locked up and an engine stall. Thus, the fuel economy ofthe car can be improved.

FIG. 2 shows a block diagram of an embodiment for achieving the systemshown in FIG. 1. In a car according to the present embodiment, a targetdriving torque is calculated based on a depression stroke on theaccelerator pedal, and the output torque of the engine and thetransmission ratio of the automatic transmission are controlled so thatthe target driving torque value can be produced from the output shaft.

A target driving torque operating unit 7 has a map which shows therelationship between the car speed and the driving torque for eachdepression stroke of the accelerator pedal. The driving torque map isstored in the memory after this has been measured experimentally inadvance. The driving torque map will be explained in detail later withreference to FIG. 4. The depression stroke of the accelerator pedal andthe car speed are detected by an accelerator device 10 and a car speedsensor 11 respectively, and they are inputted to the target drivingtorque operating unit 7. The accelerator 10 produces an electric signalaccording to the depression stroke of the accelerator pedal, by acombined use of the accelerator pedal and a potentiometer. The car speedsensor 11 is a conventional speed sensor.

The target driving torque operating unit 7 retrieves a driving torquemap and obtains a target driving torque determined by an input value. Anoperating unit 8 determines the target driving torque and the targetengine torque based on the target transmission ratio. Assuming there isno transmission loss (transmission efficiency=100%), a relationship ofT_(o) =T_(e) ×i exists, where T_(o) is a driving torque, T_(e) is anengine output torque and "i" is a transmission ratio. At first, thevalue of the target engine torque T_(e) is selected to have an optimumfuel economy, and the transmission ratio i is decided based on thetarget engine torque T_(e) and the target driving torque T_(o).Alternately, the value of the target engine torque T_(e) can be selectedso that the air-fuel ratio of the mixture becomes the target value andthen the transmission ratio i is decided based on the target enginetorque T_(e) and the target driving torque T_(o). The former case is atorque control attaching great importance to fuel economy and the lattercase is a torque control attaching great importance to the exhaustemission control.

When the target engine torque has been decided, a throttle value openingdeciding unit 9 refers to the map of the relationship between the enginespeed and the engine torque at the target-air-fuel ratio, to decide atarget throttle value opening which produces a given target enginetorque and which brings about the best efficiency of the engineoperation. The torque variation control unit 4 produces a throttle valvecontrol signal to be gained by the target throttle value opening andapplies the throttle value control signal to the throttle actuator 52 ofthe engine torque control unit 5. The throttle actuator 52 is anactuator for driving the throttle value according to the control signal.The torque variation control unit 4 produces a command for changing thetransmission ratio or a command for changing the target air-fuel ratio,in response to the detection of a torque variation by the torquevariation detecting unit 3. The command of the transmission ratio isgiven to the transmission ratio control actuator 6.

FIG. 3 is a block diagram of the power train system for a car in whichthe control unit shown in FIG. 2 is applied. The torque variationdetecting unit 3 (excluding the torque sensor), the torque variationcontrol unit 4, the target driving torque operating unit 7, theoperating unit 8 and the throttle valve opening deciding unit 9 of FIG.2 are stored within a controller 15. Each functional block within thecontroller 15 may be realized by an individual electric circuit, and allor part of the functional blocks may be realized by a conventionalcomputer which is operated by a program. A depression stroke of theaccelerator pedal 10, a car speed signal from the car speed sensor 11, atorque signal from a shaft torque sensor 12, an air-fuel ratio signalfrom an air-fuel ratio sensor 13, an output shaft speed Nt and an inputshaft speed Ne of a torque converter 14 and a throttle opening 8 areinputted to the controller 15. The controller 15 controls an engine 16and a transmission 17 by using the control system shown in FIG. 2. Theengine control is carried out by a combination of throttle actuators (amotor, a throttle valve and a throttle sensor) provided on an air intakepipe of the engine 16 and a fuel injection valve 20. The transmissioncontrol is carried out by a lockup control actuator 21 for carrying outa lockup control and a speed change control actuator 22. A Nox reductioncatalyst 24 is disposed in exhaust pipe 23 for emission controlling incontrolling of the air-fuel ratio. The present invention can also beapplied to car equipped with an exhaust emission control system whichuses an oxyde catalytic converter or a three-way catalytic converter.When the control actuator of the governor lever of the fuel injectionpump is used instead of the throttle actuator 19, this system can alsobe applied to the control of a diesel engine car.

FIG. 4 is a map for showing an optimum relationship between the carspeed and the driving torque stored in the target driving torqueoperating unit 7 shown in FIG. 2. In FIG. 4, the horizontal axis showsthe car speed and the vertical axis shows the driving torquecorresponding to the accelerator pedal angle. The hatched area in themap shown an excess driving torque portion, and it is necessary toescape from this area to reduce the weight of the driving system and tosecure an optimum drivability. A range A separated by a broken line is atake-off marginal torque area for setting a large driving torque to havean improved startability of the car, prepared by considering the carinertia at the time of starting. A range B separated by two broken linesis an acceleration torque area which changes depending on theaccelerator pedal stroke (such as 5/5: maximum stroke, 4/5 partialstroke, etc.) as shown. This area is a driving torque necessary forgiving an acceleration to the engine after the car has started until thecar speed reaches the target car speed smoothly. A range C is a carspeed constant torque portion for outputting a driving torque whichmatches the running resistance to enable the driver to achieve aconstant run speed as he desires. An ideal driving pattern by an expertdriver is predetermined and set in the map shown in FIG. 4.

The throttle opening deciding unit 9 shown in FIG. 2 stores the map ofthe relationship between the engine speed and the engine torque for eachvalue of the air-fuel ratio. FIG. 5 shows a result of the map of therelationship between the engine speed and the engine torque convertedinto a map of the relationship between the air-fuel ratio and the enginetorque under the condition of a constant speed. It is understood fromFIG. 5 that the engine torque changes depending on the air-fuel ratio.For example, if the air-fuel ratio is changed to a lean side when thecar is being driven at the air-fuel ratio of 14.5, the engine torquereduces to about 1/2 of the torque at the air-fuel ratio 14.5. When achanged engine torque value has been decided, a value of the air-fuelratio to be controlled can be decided from the map of the relationshipbetween the engine speed and the engine torque for each air-fuel ratio.The control of the engine torque can be executed with a relatively highprecision by this air-fuel ratio control.

Next, the control method according to the present invention in a carusing the CVT (Continuously Variable Transmission) shown in FIG. 3 willbe explained with reference to FIG. 6. The control flow shown in FIG. 6is executed by a control program which is stored in the microcomputerwithin the controller 15.

At Step 301, the current depression stroke of the acceleration pedal andthe current car speed are read from the accelerator 10 and the car speedsensor 11. At Step 302, the target driving torque operating unit 7refers to the map which shows the relationship between the car speed andthe driving torque and obtains a target driving torque which isdetermined by the accelerator pedal angle and the car speed value. AtStep 303, a decision is given whether the current car speed is nothigher than 20 km/h or not. The value of this reference car speed is thecar speed when the engaging of the lockup clutch is started. This valueis one example, and the present invention does not limit the referencevalue to 20 km/h. When the car speed is the reference car speed of 20km/h or lower, the lockup clutch is disengaged and the automatictransmission 17 transmits the torque by the fluid (through the torqueconverter). When power is to be transmitted through the torqueconverter, at Step 317, the transmission ratio at which the targetdriving torque is to be generated and the throttle opening and theair-fuel ratio at which the fuel consumption rate is minimum aredecided, by considering the operation characteristics of the torqueconverter.

When the current car speed is not equal to or lower than 20 km/h, atStep 304, the lockup actuator 21 operates so that the lockup clutchconnects the engine output shaft directly with the input shaft of theCVT.

The torque variation detecting unit 3 is monitoring the shaft torquefrom the shaft torque sensor 12, and calculates the change quantity ofthe shaft torque per unit time or the torque variation quantity, at Step305. At Step 306, a decision is made whether the torque variationquantity is larger than the reference value m or not. The referencevalue m is decided in advance by considering the torque variationquantity corresponding to the level of a booming noise generated.

when the torque variation quantity is equal to or smaller than thereference value m, a decision is made that no booming noise hasoccurred. At Step 307, the following normal control is carried out. Theoperating unit 8 decides the target engine torque based on the targetdriving torque and the target speed change rate. When the target enginetorque has been decided, the throttle valve opening deciding unit 9refers to the map of the relationship between the engine speed and theengine torque at the target air-fuel ratio, produces a given targetengine torque and decides the target throttle valve opening and thespeed change rate which provide an optimum efficiency of the engineoperation. A maximum efficiency curve is shown in the map which showsthe relationship between the engine speed and the engine torque. Suchmap is shown in FIG. 38.

The torque variation controlling unit 4 produces a throttle valvecontrol signal for the target throttle valve opening to obtain andapplies the throttle valve control signal to the throttle valve controlactuator 19. The command of the transmission ratio is applied to thetransmission ratio control actuator 22.

When the torque variation quantity has exceeded the reference value m,"1" is set to the flag within the control flag 15 at Step 308. When theflag shows "1", this means that the torque variation has exceeded thereference value m. When the torque variation value has exceeded thereference value m, the engine torque must be lowered to prevent abooming noise. At Step 309, a target engine torque (an absolute value)according to a torque variation quantity is decided. The relationshipbetween the torque variation quantity and the target engine torque isexperimentally decided in advance and is stored in the memory (notshown) within the controller 15. This is an almost inverse proportionalrelationship.

At Step 310, a decision is made whether the target engine torque iswithin the air-fuel ratio control area or not. A map of an equi-air-fuelratio having the engine torque and the engine speed as parameters isreferred to and a decision is made about the air-fuel ratio area basedon the target engine torque and the output of the engine rotation sensor25. When the air-fuel ratio area is known, a decision is made aboutwhether this area is within the air-fuel ratio control area or not. Theequi-air-fuel ratio map is stored in the memory in advance. An air-fuelratio control area is indicated in the equi-air-fuel ratio map inadvance.

At Step 311, a throttle opening on the maximum efficiency curve isobtained which produces a given target engine torque by referring to themap of the relationship between the engine speed and the engine torquewithin the throttle value opening deciding unit 9, and this throttleopening is set as a target throttle opening. At Step 312, a map of therelation between the engine speed and the engine torque for eachair-fuel ratio is referred to and a target air-fuel ratio is decided.

At Step 313, a target speed change rate is decided based on the ratio ofthe target driving torque to the target engine torque. At Step 314, thethrottle actuator 19 is operated to control the fuel injection valve 20according to the target air-fuel ratio, and the transmission ratioactuator 22 is operated according to the target transmission ratio.

When a decision has been made at Step 310 that the target engine torqueis not the air-fuel ratio control area, at Step 315, a map closest tothe lean side (with a large value of the air-fuel ratio) is read fromthe map of the relationship between the engine speed and the enginetorque for each air-fuel ratio within the throttle valve openingdeciding unit 9. Next at Step 316, a throttle valve opening on themaximum efficiency curve is obtained which produces a given targetengine torque by referring to the map. Then, Step 313 and subsequentsteps follows.

FIG. 7 shows the operation data of FIG. 6. When the accelerator pedalangle has changed from A to B, the throttle opening opens from the stateof 1/8 of the part throttle to the full opening 8/8, and thetransmission ratio moves to the lower side so that the change of theaccelerator pedal angle and the change of the driving torque becomeproportional to each other. However, when the transmission has beenlocked up, the shaft torque rises suddenly to cause a vibration in thelow engine speed area. To avoid this problem, when a sudden rise of theshaft torque has been detected, the air-fuel ratio of the engine is setto be large (lean mixture) to lower the engine torque, and at the sametime, the speed change rate is set lower, to improve the fuel economyand drivability of the car, while maintaining the driving torque.

FIG. 8 is the control flow of FIG. 6 expressed in a driving force linediagram. Solid lines show driving forces by accelerator pedal angles atthe air-fuel ratio of 14.7. Broken lines show driving forces byaccelerator pedal angles at the air-fuel ratio of 22.0. Numerals 0.5,1.3 and 1.6 show representative speed change rates, and there existunlimited number of speed change rates in the case of a stagelesstransmission such as the CVT. When the accelerator pedal angle ischanged from A to B, the driving force of B is required. Since thedriving force of B coincides with the driving force of B₁ and thedriving force of B₂, the driving force of B₁ at which the throttleopening is the full open is selected. When a torque variation occurs, itis necessary to lower the engine torque, so that the driving force isshifted to the position of B₂ at which the air-fuel ratio is large, andthus the engine can maintain an optimum fuel consumption area.Thereafter, the driving force is shifted to the driving force C₁ or C₂which matches the running resistance to maintain a desired car speed.The car speed under the conditions of B₁ and B₂ is at the position of Band the car speed under the conditions of C₁ and C₂ is at the positionof C.

FIG. 9 shows another embodiment of the transmission which can be loadedon the car to which the control unit and the control method of thepresent invention are applied. FIG. 9 shows two sets of CVT unitsconnected together through a gear unit to expand a controllable range ofthe transmission ratio. An output shaft 41 of a fluid coupling 40 iscoupled to a stageless continuous variable transmission 42 and is linkedto an output shaft 45 through a gear 43 and a clutch 44. The gear 43 anda gear 46 are designed to rotate in a pair. The gear 46 is connected toanother stageless transmission 47 of a belt system and is linked to theoutput shaft 45 through a clutch 48. A transmission ratio of thestageless transmission 42 can be obtained by engaging the clutch 44 anddisengaging the clutch 48. By engaging the clutch 48 and disengaging theclutch 44, a transmission ratio of a combination of the stagelesstransmission 42 and the stageless transmission 47 can be obtained. Whenmore stageless transmission of belt system are combined in this system,an automatic transmission with more combinations of transmission ratioscan be realized.

FIG. 10 shows efficiency characteristics of the torque converter. Thehorizontal axis shows a speed ratio which is a ratio of the output shaftspeed Nt to the input shaft speed Ne of the torque converter, and thevertical axis shows an efficiency n. Efficiency changes according to theabove speed ratio, and therefore, when the speed ratio is small, theefficiency is poor and the fuel economy is aggravated as a result.Accordingly, it is desirable to control the engine torque and the speedratio to avoid the low efficiency area (below n.sub.η).

FIG. 11 is a control flow chart for operating the torque converter at ahigh efficiency condition. First, at Step 50, an accelerator pedal angleα, an input shaft speed Ne, an output shaft speed Nt and a car speed Vspare read. Next, at Step 51, a speed ratio e is obtained based on therate of the above output shaft speed Nt to the input shaft speed Ne(that is, Nt/Ne). Next, at Step 52, a maximum accelerator pedal angleα_(max) is read. At Step 53, a target driving torque T_(tar) is obtainedfrom α·T_(max) /α_(max). At Step 54, an engine torque T_(e) is obtainedfrom a function g(θ) of the throttle opening θ. Values obtained at theSteps 52 to 54 are used later when a speed ratio is calculated. At Step55, a decision is made whether the speed ratio e is equal to et+k orabove, where k is a constant and et is a marginal speed ratio. In otherwords, a margin of k is provided in addition to the marginal speed ratioso that the speed ratio does not exceed the marginal speed ratio due tothe inertia of the rotation mass. If e is equal to or larger than et+k,at Step 56, a decision is made whether flg is 1 or not. If flg is not 1,at Step 57, a throttle valve opening θ is obtained as a product of theaccelerator pedal angle α and kk (which is a constant that takes achange h (i) at the speed change rate i), and the result is outputted.At Step 58, the speed change rate i is calculated. Last, at Step 59, thecurrent throttle valve opening θ is inputted to θ_(n-1). When flg is 1,at Step 60, kkk is added to the throttle valve opening θ for each task.Next, at Step 61, a decision is made whether the throttle valve openingθ for fail-safe has become the maximum throttle valve opening θ_(max) ornot. If the throttle valve opening θ has become the maximum throttlevalve opening θ_(max), the throttle valve opening θ is replaced by themaximum throttle valve opening θ_(max) at Step 62. At Step 63, flg isset to zero, and Steps 58 and 59 follow. If e has become smaller thanet+k, at Step 64, flg is set to 1. Further, at Step 65, the throttlevalve opening θ is replaced by the previous throttle valve openingθ_(n-1), to ensure that the throttle valve opening does not becomelarger and that the speed change rate does not fall under the lowefficiency area. Then, Steps 58 and 59 are carried out. The flow of FIG.11 is executed by a microcomputer of the controller 15 shown in FIG. 3according to a control program. The efficiency operation control of thetorque converter shown in FIG. 11 can be combined with the control of abooming noise shown in FIG. 6.

FIG. 12 shows operation data of the flow shown in FIG. 11. When thedriver changes the depression stroke of the accelerator pedal from thelevel A to the level B to change the throttle opening to near the fullopening, and at the same, to change the transmission ratio from 0.5 toabout 1.2, the speed ratio is lowered to below the target speed ratioet. If the speed ratio is controlled by a feedback as shown in FIG. 11,the throttle valve opening and the transmission ratio as shown by brokenlines are obtained and the fuel economy improves without going downbelow the target speed ratio et.

FIG. 13 shows the control operation of FIG. 12 in the line diagram ofdriving force. When the driver requests the driving torque of B, thedriving torque of B₁ at the transmission ratio of 1.2 in the fullopening the throttle valve (8/8) is most desirable from the viewpoint ofthe fuel economy. However, in this case, the torque converter slips whenthe car is running up along a sharp slope, and the fuel consumptionbecomes in a low efficiency area, resulting in a poor fuel economy. Toavoid this situation, the throttle valve is closed to shift thetransmission ratio to the lower side, to escape the low efficiency area.Then, the transmission ratio is gradually shifted to the higher side tomove the driving torque of C to C₁ at which the fuel economy is better,and then the car speed is stabilized there.

FIG. 14 shows a configuration of the hybrid automatic transmission towhich the present invention can be applied. An engine 60 is directlyconnected with a torque converter 62 of an automatic transmission 61shown by a broken line. The torque converter 61 is directly connectedwith an input side gear 63 for a first speed level and an input sidepulley 64 of a continuous variable transmission for a second speed levelafterward. An output side gear 65 for the first speed level and anoutput side pulley 66 of the continuous variable transmission for thesecond speed level and afterward are directly connected with adifferential gear 69 through a clutch 67 and a clutch 68 respectively,to transmit the torque generated by the engine 60 to wheels 70.

FIG. 15 shows a driving force diagram of the case where the hybridautomatic transmission of FIG. 14 is used. A solid line A shows a lineof a maximum driving force when the throttle valve is full open. Ashaded portion of the low car speed area is a first speed level areawhen the gear is used, and other areas are the second speed level andsubsequent speed level areas where the continuous variable transmissionis used. When the speed reduction ratio (for example 2.5) of the shaftof the first speed level is matched with the maximum speed reductionratio of the continuous variable transmission of the second speed leveland subsequent speed level area, a smooth car speed change can berealized without a shock of the speed change between the first speed andsecond speed levels.

FIG. 16 shows a diagram of the oil pressure pump control system forcontrolling the torque converter having a lockup clutch and thetransmission. In FIG. 16, an arrow A shows a transmission of power(torque), an arrow B shows a flow of oil and an arrow C shows anelectric signal. A power generated from an engine 71 is transmitted towheels 74 through a torque converter 72 and a speed changing mechanism73. A signal of a throttle sensor 75 provided in the engine 71 and anengine speed signal are inputted to an oil pressure controller 76, todrive an electrically-driven oil pump 77. An oil pressure switch 78 isprovided for feeding back the oil pressure to always realize an optimumoil pressure to meet the operating condition. Oil is sent from theelectrically-driven oil pump 77 to an oil pressure control circuit 79 tocontrol the speed change and lockup. Oil is supplied from the oil pan80. By the above arrangement, reduction of the oil pressure in the lowspeed area due to a locked-up driving can be prevented.

FIG. 17 is a configuration diagram of a motor integrated with a starter,an oil pump and a cooling fan. A ring gear 82 directly connected to anengine 81 is directly connected to a pump 85 of a torque converter 84provided in an automatic transmission 83. The torque from the pump 85 istransmitted to a turbine 86, and an impeller controllingly sends the oilwhich flows from the pump 85, to the turbine 86. The turbine 86 and anoutput shaft 88 are directly connected with each other. Amechanically-driven oil pump 89 is driven by the rotation of-the outputshaft 88. This is used as a fail-safe when an electrically-driven oilpump 90 is in fault. The structure of an integrated type motor 91includes a gear 92 for starting the car, a magnet switch 93, a coolingfan 94, a lever 95 for starting the car and a rotor 96. The oil pressurecontroller 76 controls the oil pressure at the time of car starting andlockup, and, after the car has been started, rotates the rotor 96 todrive the cooling fan 94 and the electrically-driven oil-pump 90. Thecooling fan 94 prevents the rise in temperature of the transmission 83due to heat generated at the time when the lockup clutch 98 slips. Theelectrically-driven oil pump 90 absorbs oil from the oil pan 80 andsupplies oil of an optimum pressure to the oil pressure circuit 79.

Another embodiment of the present invention will be explained in detailbelow.

FIG. 18 shows one embodiment of the present invention. A torquegenerated by an engine 101 is controlled by three units of an ignitionunit 102 for controlling an ignition timing, a fuel unit 103 forcontrolling a fuel quantity ratio or the fuel flow of the cylinders anda throttle valve control unit 104 for controlling a fuel quantity. Anincrease or decrease of the driving torque in an automatic transmission105 is controlled by a lockup mechanism 106 and a speed changingmechanism 107. In an automobile car equipped with the torque controlapparatus as described above, a signal of a torque variation detectingunit 109 which obtains a torque variation of the driving system from thesignal of a torque sensor 108 is inputted to a torque control unit 110for controlling a generated torque and a torque transmission coefficientcontrol unit 111, to prevent a booming noise at the time of controllinga lockup.

FIG. 19 shows a further detailed configuration of the embodiment shownin FIG. 18. One or two CPU's 121 (Central Processing Units) are mountedon a controller 120. When two CPU's are mounted, control of thetransmission ratio and control of the air-fuel ratio are carried outseparately by these two CPU's. The controller 120 is supplied with anaccelerator pedal angle signal α from an acceleration sensor 122, an airflow rate signal Q_(a) from an air flow rate sensor 123, a throttlevalve opening signal θ from a throttle valve sensor 124, an air-fuelratio A/F signal from an air-fuel ratio sensor 125, a car speed signalV_(sp) from a car speed sensor 126, an engine speed signal Ne from acrank angle sensor 127, a torque variation signal from the torque sensor108 and a wheel speed signal V_(fr) from a wheel speed sensor 128. Thecontroller 120 controls the ignition unit 102, the fuel unit 103, thethrottle valve controlling unit 104, the lockup mechanism 106 and thespeed changing mechanism 107, to meet both drivability and the fueleconomy.

FIGS. 20 to 22 show main flowcharts of the control of the engine and thetransmission according to another embodiment of the present invention.The transmission of the present embodiment has a plurality of fixeddifferent gear ratios. At step 200, an accelerator pedal angle α, a carspeed V_(sp) and an engine speed Ne are read. At step 201, based on amap of the accelerator pedal angle for each car speed level, a maximumaccelerator pedal angle α_(max) is calculated from the function f of a,maximum value T_(max) of the driving torque and a car speed V_(sp)corresponding to each accelerator pedal angle. At step 202, a targetdriving torque T_(tar) =α*T_(max) /α_(max) is obtained by calculation.At step 203, an estimated engine speed N_(n) and an estimated drivingtorque T_(n) are calculated. For example, in the case of the first speedlevel, an estimated engine speed N₁ at the first speed level=V_(sp)*i_(end) (the final speed reduction ratio)*i₁ (a speed reduction ratioat the first speed level)*k₁ (a correction coefficient) is obtained, anda maximum engine torque Te_(max) at the above estimated engine speed isobtained from g (N₁) (where N₁ is an engine speed) based on the map forshowing the relationship between the engine speed and the engine torque.Then, an estimated driving torque T₁ =Te_(max) ×i_(end) (the final speedreduction ratio)*i₁ (a speed reduction ratio at the first speed level)is calculated. The above calculation is carried out for four speedlevels if the transmission has four speed levels.

At step 204, a decision is made whether there is a torque variation ornot, depending on whether the flag T_(flg) for showing the torquevariation is "0" or not.

When the flag T_(flg) is "0", there is no torque variation and the stepmoves to X (FIG. 21). When the flag T_(flg) is "1", there is a torquevariation, and the step proceeds to Y (FIG. 22). In FIG. 21, at step205, the target driving torque T_(tar) obtained in FIG. 20 and anestimated driving torque T₄ are compared. When T_(tar) is not higherthan T₄, a speed reduction ratio gear (4) of the fourth speed level isinputted to i_(out) at step 206. At step 207, shift points S₀₁ A=1 andS₀₁ B=0 of the fourth speed level are inputted. When the T_(tar) islarger than T₄ at the step 205, a decision is made at step 208 whetherthe engine speed Ne does not exceed a speed limit (for example, 6,400rpm) or not and a over running of the engine is prevented. At step 209and step 210, shift points are decided in the same manner as in the step205. At step 211 and step 212, the same processing as in the step 208 iscarried out. The processing same as the one for the above-describedfourth speed level is carried out for the third speed level at steps 213and 214, for the second speed level at steps 215 and 216 and for thefirst speed level at steps 217 and 218, respectively. At step 219, atarget engine torque Te is obtained from T_(tar) /(i_(out) *i_(end)). Atstep 220, a throttle valve opening θ is obtained from the engine speedNe and the map of the throttle valve opening θ of the engine torque Te.At step 221, the throttle valve opening θ and the shift points S₀₁ A andS₀₁ B are outputted. In FIG. 22, at step 222, the current shift point gis calculated based on the shift point signals S₀₁ A and S₀₁ B. At step223, a decision is made whether the current shift position g is thefirst speed level or not. The step returns when g is the first speedlevel. When q is not in the first speed level, g-1 is calculated at step224 and the position is shifted down. At step 225, a speed reductionratio g_(ear) (n) which meets the shift point is inputted to i_(out). Atstep 226, an engine torque Te is calculated in the same manner as instep 219. At step 227, a target air-fuel ratio (A/F) which meets theengine torque Te is obtained from the map of the relationship betweenthe engine torque Te in which the engine speed Ne is a parameter and thetarget air-fuel ratio (A/F), and the obtained target air-fuel ratio(A/F) is used for an engine control to be described later. The step thenreturns to Z in FIG. 21.

FIG. 23 shows a flowchart of fuel and ignition controls in the carcontrol unit according to the present invention. At step 228, an airflow rate Qa, an engine speed Ne, a throttle valve opening θ and anair-fuel ratio A/F are read. At step 229, Qa/Ne and dθ/dt arecalculated. Next, at steps 230 and 231, a fuel injection amount T_(p)and an ignition timing adv are obtained by the following expressionsrespectively:

    ______________________________________                                        Tp =     A.sub.1 (correction coefficient) * f.sub.1 (Qa/Ne, Ne)                        * f2 ((A/F).sub.o) (air-fuel ratio correction                                 coefficient) + ΔA/F (air-fuel ratio correction                          quantity) + f.sub.3 (dθ/dt) (acceleration                               correction quantity)                                                 adv =    A.sub.2 (correction coefficient) * g.sub.1 (Q.sub.a /Ne, Ne) +                g.sub.2 (dθ/dt) (acceleration correction                       ______________________________________                                                 quantity)                                                        

Next, at step 232, an actual air-fuel ratio A/F is compared with thetarget air-fuel ratio (A/F_(o)). If they coincide with each other, thestep returns. If they do not coincide, an air-fuel ratio correctionquantity ΔA/F is obtained at step 233, and the step returns.

Regardless of whether the above-described control for the restriction ofa booming noise is being carried out or not, it is necessary todisengage the lockup clutch at the time when the car starts running orwhen the speed is being changed if the transmission has the fixed gearratios, and it is necessary to disengage the lockup clutch at the timewhen the car starts running or when the car is running at a low speedrate in the case of the CVT. This is necessary to prevent an enginestall and to reduce a shock due to a speed change.

FIGS. 24 to 27 show flowcharts when a lockup clutch is to be disengaged.FIG. 25 shows a case when a lockup clutch at the time of a low-speedrunning of a car is to be disengaged. At step 244, a car speed V_(sp) isread, and at step 245, a decision is made whether the car speed V_(sp)is not higher than a set car speed V₁₀ (about 10 km/h) or not. When theV_(sp) is not higher than the set car speed V₁₀, a duty ratio 1 u of thelockup is obtained by a car speed V_(sp) *k₂ (a correction coefficient)at step 246. When the V_(sp) is higher than the V₁₀, a maximum duty rateD_(max) is inputted as 1 u at step 247. At step 248, a duty signal 1 uis outputted. FIGS. 26 and 27 show the case for disengaging the lockupclutch at the time when the car speed is being changed. At step 249, aspeed Nt of a turbine (an output shaft of the torque converter), a carspeed V_(sp) and shift point signals S₀₁ A and S₀₁ B are read. At step250, a gear ratio i, including the gear ratio during a speed change, isobtained by k₃ (correction coefficient)*V_(sp) /Nt. Next, at step 251,the current shift point g_(n) is obtained from the shift point signalsS₀₁ A and S₀₁ B. At step 252, the last shift point g_(n-1) is comparedwith the current shift point g_(n). If the g_(n-1) and g_(n) are not thesame, the process proceeds to step 253, where a decision is made whetherthe current shift point g_(n) is larger than the preceding shift pointg_(n-1). If the g_(n) is larger than the g_(n-1), that is, if theshift-up was made, the process proceeds to A. If the g_(n) is smallerthan the g_(n-1), that is, if the shift-down was made, the processproceeds to B. In FIG. 26, in the case of A (that is, the shift-up), atstep 254, the gear ratio j obtained at the step 250 is compared with atarget gear ratio j (g_(n-1))-k₄ (a correction coefficient) when thecontrol is to be started. If the j is larger than the j (g_(n-1))-k₄,the process is looped. When the j becomes smaller than the j(g_(n-1))-k₄ after repeating the loop, the process goes to step 255,where a minimum duty ratio D_(min) for disengaging the lockup clutch isinputted as the duty ratio 1 u of the lockup. Next, at step 256, thegear ratio j compared with a target gear ratio i (g_(n))+k₄ (acorrection coefficient) when the control is to be ended. If the j issmaller than the i (g_(n))+k₄, the process is looped. When the j becomeslarger than the i (g_(n))+k₄ after repeating the looping, the processgoes to step 257 and a maximum duty ratio D_(max) for engaging thelockup clutch is inputted as the duty ratio of the lockup. In the caseof B (that is, the shift-down), the steps 258 to 260 are executed in thesame manner, and a decision is made about the speed change and thusdisengaging the lockup clutch. Last, at step 261, the current shiftpoint g_(n) is inputted to the shift point g_(n-1) of the precedingtime, and the process ends. FIG. 27 shows a flowchart of the disengagingof a lockup clutch when a sudden brake has been applied. At step 262, awheel speed V_(fr) at the driving side is read. At step 263, the V_(f) ris compared with a set wheel speed V_(fro). If the wheel speed V_(fr) isnot higher than the set wheel speed V_(fro), a decision is made that thewheels have been locked as a result of jamming on the brakes. At step264, a minimum duty ratio D_(min) for disengaging the lockup clutch isinputted as the duty ratio 1 u of the lockup. If the V_(fr) is largerthan the V_(fro), a maximum duty ratio D_(max) for engaging the lockupclutch is inputted as the duty ratio 1 u of the lockup at step 265. Atstep 266, the duty ratio 1 u of the lockup is outputted.

FIG. 28 shows a timechart for starting the engaging of the lockupclutch. After the driver has started the engine while the shift lever ofthe automatic transmission is positioned in N (neutral) or P (parking),he monitors, based on an N-D range signal, to check if the shift statehas been changed to a D (drive) range state. Normally, the car speed iszero km/h in the N (neutral) or P (parking) state because the brakepedal is kept being depressed in this state. The engine speed in thiscase is about 700 rpm, which is an idle speed. When the driver releasesthe brake pedal and, at the same time, the N-D range signal has beenchanged to the D range, the torque of the torque converter increases anda shaft torque which overcomes the running resistance and car inertiaweight occurs. Then, the car starts running and the car speed increases.When the stroke of the acceleration pedal is suddenly changed from thisstate (for example from 0/8 to 1/8), the throttle valve is opened toalmost the full open state to improve fuel economy with boost operationof the engine. In this case, an acceleration correction interruptionsignal k_(i) is being monitored. When an acceleration correction (k_(i)=1) has been inputted, a lockup signal 1_(u) =1 is outputted to engagethe lockup clutch. With the above-described arrangement, when a shafttorque has changed, the air-fuel ratio and the transmission ratio, forexample, are controlled to prevent a variation of the shaft torque asshown by a broken line.

FIG. 29 shows a flowchart for controlling the starting of the engagementof the lockup clutch. At steps 200 and 201, an N-D signal and anacceleration correction interruption signal ki are read respectively. Atstep 202, a decision is made whether the shift lever is in the D rangeor not. If the shift lever is in the D range, a decision is made whetherthe k_(i) is 1 or not at step 203. if the k_(i) is 1, the lockup isallowed, and at step 204, a lockup engagement signal 1u=1 is outputted.If the decision is "No." at the steps 202 and 203, the process proceedsto step 205, where a lockup cancellation signal 1u=0 is outputted, andthe process is returned.

FIG. 30 shows a comparative timechart for comparing efficiencies betweenthe conventional method in which no lockup is included (shown in brokenlines) and the low boost operation without a lockup (shown in solidlines). In the case of the broken lines, the throttle valve openingchange corresponds to a change of the accelerator pedal angle at theratio 1:1 and the transmission is in the low gear ratio. Therefore, achange of the shaft torque is small. However, since the opening of thethrottle valve is small, the engine efficiency is low. Further, theefficiency of the torque converter is also low so that the fuel economyis poor. On the other hand, in the case of the solid lines, the throttlevalve opens to the full for a change of the pedal stroke so that theengine efficiency becomes the highest. However, since the shaft torqueis matched to the conventional method, the transmission is in the highgear ratio. Thus, the efficiency of the torque converter becomes worsethan that according to the conventional method. Nonetheless, since theefficiency of the engine is the highest, the fuel economy is better thanthat according to the conventional method.

FIG. 31 shows a comparative timechart for comparing the efficiencies ofthe low boost operation between the cases with and without (shown insolid lines) the lockup. In both the broken lines and solid lines, thethrottle valve is opened to the full for a change of the acceleratorpedal stroke so that the engine efficiency is the highest. However, inthe case of the solid lines, a slipping of the torque converter occursand the shaft torque increases. Therefore, when the shaft torque same asthat of the broken lines is to be outputted, the transmission is in thehigh gear ratio side. In other words, the efficiency of the torqueconverter is lowered to the worst direction. On the other hand, in thecase of the broken lines, the transmission ratio is at a lower gear sidethan that of the solid lines. Thus, the fuel economy is improvedsubstantially as the efficiency of the torque converter becomes thehighest although the engine speed is a little higher. However, since theshaft torque varies and the drivability is aggravated, the fuel economycan not be achieved.

FIG. 32 shows a comparative timechart for comparing the efficiencies ofthe low boost operation with a lockup between the case for controllingthe variation (shown in solid lines) and the case where there is nocontrol of the variation (shown in broken lines and one-dot chainlines). In the case of the solid lines, the fuel economy is good asshown in FIG. 32 but the shaft torque changes. In the case of the brokenlines where there is the control of torque variation, the state oftorque variation is decided from a time change Δt of the shaft torque,and when the torque variation has exceeded target torque variationquantities T_(min) and T_(mid), an ignition timing retarding control andan air-fuel ratio control have been carried out. At first, the ignitiontiming is retarded and then the air-fuel ratio is returned. In thiscase, the engine torque becomes smaller by the ignition timing retardingcontrol and the air-fuel ratio control, and therefore, it is necessaryto change the transmission ratio to the low gear side to maintain theshaft torque requested by the driver. When a torque variation (T_(max))larger than the above torque variation quantity has occurred (as shownin the one-dot chain lines), a throttle valve control is applied to theabove air-fuel ratio control, to prevent the variation of the shafttorque. In all the cases of the solid lines, broken lines and one-dotchain lines, the fuel economy makes little difference. Thus, accordingto the present invention, it is possible to suppress torque variation incontrast to conventional systems without torque control as shown in FIG.32, and to improve fuel economy substantially in contrast toconventional systems without lockup as shown in FIG. 31.

FIGS. 33 and 34 show control flowcharts for controlling torquevariations. At step 206, an accelerator pedal stroke α and a shafttorque T are read. Next, at step 207, changes of α and T per a smalltime period, that is, Δα=dα/dt and ΔT=dT/dt, are calculated. At step208, a decision is made whether an absolute value |ΔT-Δα| is not smallerthan a target torque variation quantity T_(min) or not. If the |ΔT-Δα|is smaller than the T_(min), that is, when a decision is made that thereis no torque variation, the process goes to B and returns. If the|ΔT-Δα| is larger than the T_(min), the process proceeds to step 209 anda decision is made whether the ΔT-Δα is larger than zero or not. Whenthe ΔT-Δα is smaller than zero, a decision is made that the car speed isbeing reduced. At step 210, only the throttle valve control is carriedout from the viewpoint of the exhaust emission control. When a decisionis made at step 209 that ΔT-Δα is larger than zero, the process goes tostep 211 and a decision is made whether the ΔT-Δα is not smaller than atarget torque variation quantity T_(mid) or not. When a decision is madethat the ΔT-Δα is smaller than the T_(mid), the ignition timingretarding control is carried out at step 212. When a decision is madethat the ΔT-Δα is larger than the T_(mid), the process goes to step 213and a decision is made whether the ΔT-Δα is not smaller than a targettorque variation quantity T_(max) or not. When a decision is made thatthe ΔT-Δα is smaller than the T_(max), a fuel control (air-fuel ratiocontrol) is carried out at step 224. When a decision is made that theΔT-Δα is not smaller than the T_(max), a throttle valve control iscarried out at step 210. Then the process proceeds to the steps in FIG.34. At step 215, a target driving torque T_(out) is obtained from afunction g(α) of α. At steps 216 to 219, an ignition timing retardingquantity adn, an air-fuel ratio A/F, a throttle valve opening θ and anengine speed Ne are read. At step 220, an engine torque Te is calculatedfrom a function f (adn, A/F, θ, Ne) of the above adv, A/F, θ and Ne. Theengine torque Te may be obtained from the map using the above adn, A/F,θ and Ne. At step 221, a speed change rate i_(out) is obtained from thetarget driving torque T_(out) /engine torque T_(e), and the result isoutputted at step 222.

Next, the other embodiments of the change-over control of the lockupclutch between the engaging and disengaging (driving of the torqueconverter) of the lockup clutch will be explained. The operation of allof the following embodiments will be controlled by the computer programwithin the controller 15 in the configuration shown in FIG. 3.

FIG. 35 shows a flowchart of the system for engaging the lockup clutchif the air-fuel ratio is within a specific area. At step 401, atransmission ratio r, an output signal To of the torque sensor 12, anengine speed signal Ne and a turbine speed Nt of the torque converterare read. At step 402, a transmission ratio e=Nt/Ne is calculated. Atstep 403, a torque ratio λ is obtained from a predetermined functionλ=f(e). At step 404, an engine torque Te is obtained from Te=To/r·λ. Atstep 405, an equivalent air-fuel ratio map which uses, as parameters,the engine torque Te and the engine speed Ne, stored in the memory inadvance, is referred to, and a decision is made of the value of theair-fuel ratio (A/F) under the calculated conditions of the enginetorque Te and the engine speed Ne.

At step 406, a decision is made whether the air-fuel ratio is 20 orabove. When the air-fuel ratio is not smaller than 20, the drivingcondition is in the lean burn operation area. At step 407, a duty ratiolu for controlling the engaging of the lockup clutch is decided. Whenthe air-fuel ratio does not reach 20, a driving by the torque converteris carried out, and a duty ratio lu=0 is outputted at step 408. At step409, the lockup actuator 21 is controlled based on the given duty ratiolu.

According to the control based on the operation flow shown in FIG. 35,the fuel economy is improved substantially because the lockup clutch isengaged only in the lean burn operation area in which the air-fuel ratiois at least 20.

Instead of the processings at the steps 401 to 405, the actual air-fuelratio may also be detected directly from the output of the air-fuelratio sensor 13.

FIG. 36 shows a flowchart of the system for engaging the lockup clutchif the car driving area is within a specific area. At step 501, acurrent speed change ratio r, an output signal To of the torque sensor12, an engine speed signal Ne, a turbine speed Nt of the torqueconverter and a car speed VSP are read. At step 502, a speed ratioe=Nt/Ne is calculated. At step 503, a torque ratio λ is calculated froma predetermined function λ=f(e). At step 504, an engine torque Te isobtained from Te=To/r·λ. At step 505, a shift program map using, asparameters, the engine torque Te and the car speed V_(sp), stored in thememory in advance, is referred to and the engine torque of the lockupclutch engaging area and the car speed conditions are read. At step 506,a decision is made whether the map of the current engine torque Te andthe car speed V_(sp) is in the lockup clutch engaging area or not. Ifthe map is in the lockup clutch engaging area, a duty ratio lu forcontrolling the engaging of the lockup clutch is decided at step 507.When the map is in the lockup clutch area, in order to drive the car bythe torque converter, a duty ratio lu=0 is outputted at step 508. Atstep 408, the lockup actuator 21 is controlled based on the given dutyratio.

Next, the method for controlling the lockup clutch in the engine whichuses an Idle Speed Control (ISC) valve will be explained with referenceto FIG. 37. As shown in FIG. 3, the ISC valve 26 is disposed in parallelwith the throttle valve in the air intake system. The ISC valve 26 isused to control an increase or decrease of the intake air quantity basedon an electrical signal separate from the throttle valve. For example,there is a case where the idling speed is reduced due to driving of alarge load unit, such as an air-conditioner compressor, working duringan idling operation of the engine. In such a case, the ISC valve 26increases an intake air quantity to compensate for a drop of the idlingspeed. The use of this function of the ISC valve makes it possible tocontrol the air-fuel ratio. In other words, by controlling the ISC valveopening level or the valve opening rate, it becomes possible toaccurately control the air-fuel ratio of the mixture in the lean area.When the ISC valve is controlling the air-fuel ratio of the lean area,the control of the lockup clutch as shown in FIG. 35 is carried out.

At step 601, a valve opening angle θx of the valve 26, a state of aswitch of the air conditioner (not shown) and a state of the throttlevalve switch (not shown) are read. The throttle valve switch is theswitch for showing whether the throttle valve is open or closed (or inthe idle state), and a valve opening signal of the throttle valveactuator 29 can also be utilized. At step 602, a decision is madewhether the throttle valve switch is ON or OFF (or in the idle state).If the throttle valve switch is not in the idle state, a decision ismade at step 603 whether the switch of the air conditioner is ON or OFF.If the air conditioner is not operating, at step 604, a decision is madewhether the current valve opening angle θx of the ISC valve 26 is largerthan the previous valve opening angle θx(n-1) (where n is an integer).If the current valve opening angle is larger, a lean burn control is tobe carried out and the processings at the step 407 afterward of the flowin FIG. 35 are carried out. If the current valve opening state is thesame as the previous valve opening angle or smaller than this, theprocessings at the step 408 and afterward of the flow in FIG. 35 arecarried out.

FIG. 38 shows an engine efficiency diagram wherein the real linesrepresent the specific fuel consumption curves (g/ps·h), and the dottedlines represent the equi-horsepower curves (ps). This diagram can beutilized in the method and apparatus of the present invention. There maybe infinite number of the equi-horsepower curves in the diagram. Whenthe least fuel consumption points (dots) are traced on the infiniteequi-horsepower curves, the optimum fuel consumption operation curve(g/h(min)) as indicated by the chain line is obtained. When the engineis operated with tracing on the optimum fuel consumption operationcurve, the engine is operated in the ideal optimum efficiency. The fueleconomy can be improved when the engine is operated in the optimum fuelconsumption by controlling the air flow and the transmission ratio.

It should be noted that the present invention is not limited to theabove-described embodiments, and all the aspects that any person in thistechnical field can apply, alter or improve based on the above-describedspecification, drawings and disclosure of the claims, shall all beincluded under the scope of the present invention.

According to the present invention, there is an effect that a lockup ispossible from the time of starting the car and thus the fuel economy isimproved.

Further, according to the present invention, drivability can be securedwhen a torque variation is large, and a driving force requested by thedriver can be obtained, with a high fuel economy.

We claim:
 1. A method for controlling a car having an automatictransmission with a lockup clutch, comprising the steps of:detecting apresent air-fuel ratio of mixture introduced into an engine of said car;judging as to whether said air-fuel ratio is within a predetermineregion; and engaging said lockup clutch when said air-fuel ratio iswithin said region.
 2. A method according to claim 1, wherein saidlockup clutch is engaged when said air-fuel ratio is in more lean regionthan a predetermined value.
 3. A method according to claim 2, whereinthe step for detecting the air-fuel ratio includes a step for detectingan engine torque and an engine speed, a step for looking up apredetermined map for the air-fuel ratio with respect to the enginetorque and the engine speed as the parameters, and a step for obtainingthe air-fuel ratio from said map.
 4. A method according to claim 2,wherein the step for detecting the air-fuel ratio includes a step fordetecting an opening degree of an air flow control valve disposed inparallel with a throttle valve in an air inlet pipe of an engine, and astep for judging that the air-fuel ratio is in the lean side whendetected said opening degree of said valve is more than a predeterminedvalue.
 5. A method according to claim 2, wherein the air-fuel ratio isdirectly detected by a sensor means for measuring the air-fuel ratio. 6.An apparatus for controlling a car having an automatic transmission witha lockup clutch, comprising:means for detecting a present air-fuel ratioof mixture introduced into an engine of said car; means for judging asto whether said air-fuel ratio is within a predetermined region; andmeans for engaging said lockup clutch when said air-fuel ratio is withinsaid region.
 7. An apparatus according to claim 6, wherein said judgingmeans judges as to whether said air-fuel ratio is in more lean regionthan a predetermined value, said lockup clutch being engaged when saidair-fuel ratio is in said more lean region.
 8. An apparatus according toclaim 7, wherein said means for detecting the air-fuel ratio includessensor means for detecting an engine torque and an engine speed andmemory means for storing a predetermined map for the air-fuel ratio withrespect to the engine torque and the engine speed as the parameters,said air-fuel ratio being obtained by looking up said map.
 9. Anapparatus according to claim 7, wherein said means for detecting theair-fuel ratio includes an air flow control valve disposed in parallelwith a throttle valve in an air inlet pipe of an engine, means fordetecting an opening degree of said air flow control valve, said judgingmeans judging that the air-fuel ratio is in the lean side when detectedsaid opening degree of said valve is more than a predetermined value.10. An apparatus according to claim 7, wherein said means for detectingair-fuel ratio includes a sensor means for directly measuring theair-fuel ratio by detecting components in exhaust gas of the engine. 11.An apparatus according to claim 6, wherein said car further has anelectric oil pump driven by an electric power source and a mechanicaloil pump driven by an output shaft of said automatic transmission, saidautomatic transmission and said lockup clutch are controlled with oilpressure generated by at least one of said electric oil pump and saidmechanical oil pump.